The present invention concerns an improved safety lock mechanism, e.g. for doors.
In public premises designed to hold a large number of people it is imperative -- and in some countries obligatory and expressly required by the fire department chief or corresponding authority -- that all entrances and exits be arranged to be quickly and easily opened simultaneously, or nearly simultaneously, in the event of fire or other danger.
To eliminate the necessity of keeping a large number of service personnel in attendance to watch all entrances and exits, the number of which in some cases, such as in sports arenas, may be considerable, electrically controllable locking mechanisms have been installed. A large variety of such locking mechanisms are available and in principle they all function through cooperation between a locking bar and an electromagnet, for instance, in such a way that when an electromagnet is energized it activates the locking bar so as to move the latter in the axial direction from its door-locking position in engagement with a door frame to its door-opening position. Consequently, one single switch may control any number of doors to unlock them all simultaneously.
However, mechanisms of this kind suffer from serious drawbacks. In the event that a rapidly developing accident, such as an explosive fire, occurs in public premises holding a large number of persons, the persons inside easily panic. Crowds of people will then rush towards the exits. If the latter are not already unlocked, the masses of people will exert such a pressure on the doors that the locking bars will be prevented from moving to the door-opening position because of the large amount of friction created between the locking bars and the door frame Even if eventually it is possible to force the doors open, the opening thereof will nevertheless be considerably delayed and the evacuation of the premises will take place at a pace that is unsatisfactorily low, resulting in the evident jeopardising of people's lives.